Recently, there have been broadly used organic electrophotographic photoreceptors (hereinafter, also denoted simply as organic photoreceptor or photoreceptor) containing an organic photoconductive material, as an electrophotographic photoreceptor. Organic photoreceptors are advantageous over other photoreceptors in the respects that of a material corresponding to various kinds of light sources of visible to infrared light are easily developable, a material having no environmental pollution can be chosen and production cost is low, but still have some problems that mechanical strength is low, deterioration or flaws of the photoreceptor surface easily occurs in copying or printing of a large number of sheets and durability is insufficient.
To solve problems such as durability of an organic photoreceptor being insufficient, it has been strongly sought to inhibit abrasion due to scratching by a cleaning blade. As an approach therefor have been studied techniques of providing a protective layer with a high strength on the surface of the photoreceptor or the like.
For instance, there was reported the use of a curable siloxane resin containing a colloidal silica for the photoreceptor surface (as described in, for example, JP 2000-275877A). In such a curable siloxane resin containing a colloidal silica, however, not only a curable resin with a siloxane bonding (Si—O—Si bond) but also colloidal silica which exhibits high hygroscopicity and the electric resistance of the surface layer is easily lowered, producing problems that image unsharpness or image swearing easily occurs.
In another embodiment, there was proposed a protective layer of a curable resin obtained by photo-polymerization of a compound containing an acryloyl group or the like (as described in, for example, JP 2001-125299A). In such a protective layer, a filler of a metal oxide or the like was incorporated in the curable resin, however, in the prior art, dispersibility of the filler in the curable resin was insufficient and bonding of the filler to the curable resin was weak through a hydrogen bond or the van der Waals force, so that although the strength of the curable resin was relatively high, detachment of the filler often occurred and strength as a protective layer was insufficient and such image unsharpness or image smearing was not sufficiently solved.
On the other hand, there was proposed a technique of using metal oxide particles produced via a plasma method (as described in, for example, JP 2002-229240A). It was known that such metal oxide particles produced via a plasma method were small and uniform in particle size and superior in dispersibility, as compared to convention ones, resulting in effective inhibition of leakage occurrence. However, the metal oxide particles produced via the plasma method exhibited enhanced surface activity and easily adsorbed moisture or discharge products under high temperature and high humidity, producing problems such that image unsharpness readily occurred. Further, in the prior art, a binder resin employed a linear polymeric material with a relatively low strength and the difference in strength from a metal oxide was great so that flaws easily occurred, producing problems such that filming was generated from such flaws as the starting point.